The present invention relates to stripper fingers and associated rollers used with a fuser, such as for xerographic printers.
In xerographic or electrostatographic printers commonly in use today, a charge-retentive member is charged to a uniform potential and thereafter exposed to a light image of an original document to be reproduced. The exposure discharges the charge-retentive surface in exposed or background areas and creates an electrostatic latent image on the member which corresponds to the image areas contained within the original document. Subsequently, the electrostatic latent image on the charge-retentive surface is made visible by developing the image with developing powder referred to in the art as toner. Most development systems employ a developer material which comprises both charged carrier particles and charged toner particles which triboelectrically adhere to the carrier particles. During development the toner particles are attracted from the carrier particles by the charge pattern of the image areas on the charge-retentive area to form a powder image on the charge-retentive area. This image is subsequently transferred to a sheet, such as copy paper, to which it is permanently affixed by heating or by the application of pressure. Following transfer of the toner image to the sheet, the charge-retentive member is cleaned of any residual toner that may remain thereon in preparation for the next imaging cycle.
One approach to fixing the toner image is by applying heat and pressure by passing the sheet containing the unfused toner images between a pair of opposed roller members at least one of which is internally heated. During this procedure, the temperature of the toner material is elevated to a temperature at which the toner material coalesces and becomes tacky. This heating causes the toner to flow to some extent into the fibers or pores of the sheet. Thereafter, as the toner material cools, solidification of the toner material causes the toner material to become bonded to the support member. Typical of such fusing devices are two roll systems wherein the fuser roll is coated with an adhesive material such as a silicone rubber or other low surface energy elastomers.
During the fusing process and despite the use of low surface energy materials as the fuser roll surface, there is a tendency for the print substrate to remain tacked to the fuser roll after passing through the nip between the fuser roll and the pressure roll. When this happens, the tacked print substrate does not follow the normal substrate path but rather continues in an arcuate path around the fuser roll, eventually resulting in a paper jam which will require operator involvement to remove the jammed paper before any subsequent imaging cycle can proceed. As a result it has been common practice to ensure that the print substrate is stripped from the fuser roll downstream of the fuser nip. One approach is the use of a plurality of stripper fingers placed in contact with the fuser roll to strip the print substrate from the fuser roll. While satisfactory in many respects, this suffers from difficulties with respect to both fuser roll life and print quality. To ensure an acceptable level of stripping it is frequently necessary to load such a stripper finger against the fuser roll with such a force and at such an attack angle that there is a tendency to peel the silicone rubber off the fuser roll, thereby damaging the roll to such an extent that it can no longer function as a fuser roll. Further, there is a tendency for the stripper fingers to leave fingermarks on the sheets.
There is provided a fuser for xerographic printing, stripper fingers remove the print sheet from a fuser roll. The stripper finger having a tip for stripping a lead edge of a sheet from said fuser roll. A roller assembly, positioned adjacent to said stripper finger; for engaging said lead edge of a sheet and lifting the sheet from further contact with said tip after said tip of said stripper finger strips said lead edge of said sheet from said fuser roll.